1. Field of the Art
This invention relates to a method for fabricating a solenoid device for electromagnetic valves, and more particularly to a method for fabricating a molded solenoid device which is encased in a molded synthetic resin shell.
2. Description of the Prior Art
Generally speaking, the solenoid devices which are widely used for electromagnetic valves are largely constituted by a solenoid coil wound on a bobbin of a non-magnetic material, a couple of rod-like coil terminals projected outwardly from the bobbin and connected to the head and tail ends of the winding wire of the solenoid coil, a fixed iron core fixedly mounted in an iron core chamber coaxially at the center of the bobbin, a magnetic frame of a magnetic material located to circumvent the afore-mentioned component parts, and a movable iron core disposed movably within the iron core chamber, the circumference of the magnetic frame being embedded in an insulating synthetic resin material by molding.
In order to mold the solenoid device with an insulating synthetic resin, it has been the general practice to place, within a mold cavity, a solenoid assembly except the movable iron core, and to introduce a molten synthetic resin material into the mold cavity around the solenoid assembly. When setting the solenoid assembly in position within the mold cavity, special attention needs to be paid to the coil terminals which stick out from the bobbin to such a degree as could be an obstacle to the setting operation. In this regard, the mold is usually provided with a couple of coil terminal escape holes in which the respective coil terminals are fitted when the solenoid assembly is set in molding position in the mold cavity.
The existence of the coil terminal escape holes in the mold, however, necessitates to provide some sort of blocking means for preventing leakage of the introduced molten synthetic resin through the escape holes. One of countermeasures to this problem has been to pack a sealing member into the gap space around each coil terminal in the escape hole. This method is troublesome and time-consuming to an objectionable degree. Another method which has been resorted to in this regard is to narrow the escape holes and to bring them into direct and tight contact with the coil terminals. This method also has drawbacks that it has possibilities of damaging the coil terminals or breaking the coil winding which is connected to the coil terminals.